Interdigital transducer arrangements for surface acoustic wave devices

ABSTRACT

Acoustic wave devices and interdigital transducer (IDT) arrangements for surface acoustic wave (SAW) devices are disclosed. Representative SAW devices are described herein that provide sharp transitions between passband frequencies and frequencies that are outside of desired passbands. A SAW device may include several IDTs arranged between reflective structures on a piezoelectric material and one or more additional IDTs or electrode pairs that are configured to modify the influence of parasitic capacitance, or other internal device capacitance, thereby improving steepness on the upper side of a passband as well as improving rejection for frequencies outside of the passband. The one or more additional IDTs or electrode pairs may be configured as at least one of a capacitor, an IDT capacitor, an IDT with a floating electrode, or combinations thereof.

RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 62/698,509, filed Jul. 16, 2018, the disclosure of which ishereby incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to acoustic wave devices, andparticularly to interdigital transducer (IDT) arrangements for surfaceacoustic wave (SAW) devices.

BACKGROUND

Acoustic wave devices are widely used in modern electronics. At a highlevel, acoustic wave devices include a piezoelectric material in contactwith one or more electrodes. Piezoelectric materials acquire a chargewhen compressed, twisted, or distorted, and similarly compress, twist,or distort when a charge is applied to them. Accordingly, when analternating electrical signal is applied to the one or more electrodesin contact with the piezoelectric material, a corresponding mechanicalsignal (i.e., an oscillation or vibration) is transduced therein. Basedon the characteristics of the one or more electrodes on thepiezoelectric material, the properties of the piezoelectric material,and other factors such as the shape of the acoustic wave device andother structures provided on the device, the mechanical signaltransduced in the piezoelectric material exhibits a frequency dependenceon the alternating electrical signal. Acoustic wave devices leveragethis frequency dependence to provide one or more functions.

Surface acoustic wave (SAW) devices, such as SAW resonators and SAWfilters, are used in many applications such as radio Frequency (RF)filters. For example, SAW filters are commonly used in second generation(2G), third generation (3G), and fourth generation (4G) wirelessreceiver front ends, duplexers, and receive filters. The widespread useof SAW filters is due to, at least in part, the fact that SAW filtersexhibit low insertion loss with good rejection, can achieve broadbandwidths, and are a small fraction of the size of traditional cavityand ceramic filters. As the use of SAW filters in modern RFcommunication systems increase, there is a need for SAW filters withsharp transitions between desired passband frequencies and frequenciesthat are outside of desired passbands.

SUMMARY

The present disclosure relates to acoustic wave devices, andparticularly to interdigital transducer (IDT) arrangements for surfaceacoustic wave (SAW) devices. Representative SAW devices are describedherein that provide sharp transitions between passband frequencies andfrequencies that are outside of desired passbands. In certainembodiments, a SAW device may include several IDTs arranged betweenreflective structures and one or more additional IDTs or electrode pairsthat are configured to modify the influence of parasitic capacitance, orother internal device capacitance, thereby improving steepness on theupper side of a passband as well as improving rejection for frequenciesoutside of the passband. The one or more additional IDTs or electrodepairs may be configured as at least one of a capacitor, an IDTcapacitor, an IDT with a floating electrode, or combinations thereof.

In one aspect, a SAW device, comprises a piezoelectric material, atleast one input IDT on the piezoelectric material and electricallyconnected to an input signal and ground; at least one output IDT on thepiezoelectric material and electrically connected to an output signaland ground; and an additional IDT on the piezoelectric material andelectrically connected to the input signal and the output signal,wherein the additional IDT is arranged between the at least one inputIDT and the at least one output IDT. In certain embodiments, theadditional IDT comprises an IDT capacitor. The additional IDT maycomprise a first electrode electrically connected to the input signaland a second electrode electrically connected to the output signal. TheSAW device may further comprise a first reflective structure and asecond reflective structure on the piezoelectric material, wherein theat least one input IDT, the at least one output IDT and the additionalIDT are arranged between the first reflective structure and the secondreflective structure. In certain embodiments, the at least one input IDTcomprises a plurality of input IDTs and the at least one output IDTcomprises a plurality of output IDTs. The plurality of input IDTs andthe plurality of output IDTs may be configured in an alternatingarrangement. In certain embodiments, at least one of the at least oneinput IDT, the at least one output IDT, and the additional IDT comprisesan apodized IDT.

In another aspect, a SAW device comprises a piezoelectric material, atleast one input IDT on the piezoelectric material and electricallyconnected to an input signal and ground; at least one output IDT on thepiezoelectric material and electrically connected to an output signaland ground; a first additional electrode pair on the piezoelectricmaterial and electrically connected to the input signal and the outputsignal; and a second additional electrode pair arranged between the atleast one input IDT and the least one output second IDT, wherein thesecond additional electrode pair comprises at least one floatingelectrode. The SAW device may further comprise a first reflectivestructure and a second reflective structure on the piezoelectricmaterial, wherein the at least one input IDT, the at least one outputIDT, the first additional electrode pair, and the second additionalelectrode pair are arranged between the first reflective structure andthe second reflective structure. In certain embodiments, the secondadditional electrode pair comprises a first electrode that iselectrically connected to the input signal, a second electrode that iselectrically connected to the output signal, and a floating electrode.In certain embodiments, the second additional electrode pair is notdirectly electrically connected to either of the input signal and theoutput signal. In certain embodiments, the second additional electrodepair comprises a first electrode and a second electrode and at least oneof the first electrode and the second electrode is devoid of electrodefingers. In certain embodiments, at least one of the first additionalelectrode pair and the second additional electrode pair comprises anadditional IDT. At least one of the input IDT and the output IDT maycomprise an apodized IDT

In another aspect, a SAW device comprises a piezoelectric material; afirst reflective structure and a second reflective structure on thepiezoelectric material; a plurality of input IDTs and a plurality ofoutput IDTs arranged on the piezoelectric material and between the firstreflective structure and the second reflective structure, wherein theplurality of input IDTs and the plurality of output IDTs are configuredin an alternating arrangement between the first reflective structure andthe second reflective structure; and a plurality of additional IDTsarranged between corresponding ones of the plurality of input IDTs andcorresponding ones of the plurality of output IDTs, wherein at least oneadditional IDT of the plurality of additional IDTs is electricallyconnected to an input signal and an output signal. In certainembodiments, the plurality of additional IDTs comprises at least twoadditional IDTs electrically connected to an input signal and an outputsignal. The at least one additional IDT of the plurality of additionalIDTs may comprise a first electrode that is electrically connected tothe input signal, a second electrode that is electrically connected tothe output signal, and a floating electrode. In certain embodiments, atleast one other additional IDT of the plurality of additional IDTs isnot directly electrically connected to either of the input signal andthe output signal. The at least one other additional IDT of theplurality of additional IDTs may comprise a first electrode electricallyconnected to ground and a second electrode that is a floating electrode.At least one of the plurality of input IDTs, the plurality of outputIDTs, and the plurality of additional IDTs may comprise a metallizationratio in a range of about 0.2 to about 0.8. At least one of theplurality of input IDTs, the plurality of output IDTs, and the pluralityof additional IDTs may comprise an apodized IDT.

In another aspect, any of the foregoing aspects, and/or various separateaspects and features as described herein, may be combined for additionaladvantage. Any of the various features and elements as disclosed hereinmay be combined with one or more other disclosed features and elementsunless indicated to the contrary herein.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 is a perspective view illustration of a representative surfaceacoustic wave (SAW) device 10.

FIG. 2A illustrates an example SAW couple resonated filter (CRF)structure that includes a plurality of interdigital transducers (IDTs)that are acoustically and longitudinally coupled between two reflectivestructures.

FIG. 2B is an S-Parameters plot representing simulations of the SAW CRFstructure of FIG. 2A with a variety of capacitor values.

FIG. 3 illustrates a SAW CRF structure that includes a plurality of IDTsthat are longitudinally coupled between two reflective structures.

FIG. 4A is a block diagram of a radio frequency (RF) duplexer thatincludes the SAW CRF structure of FIG. 2A.

FIG. 4B is a block diagram of an RF duplexer that includes the SAW CRFstructure of FIG. 3.

FIG. 5A is a top view of a device layout of the RF duplexer of FIG. 4A.

FIG. 5B is a top view of a device layout of the RF duplexer of FIG. 4B.

FIG. 6A is a comparison plot for isolation of RF duplexers with variousSAW CRF structures as disclosed herein.

FIG. 6B is a comparison plot for a passband of RF duplexers with variousSAW CRF structures as disclosed herein.

FIG. 7 illustrates a SAW CRF structure that includes a plurality of IDTsthat are longitudinally coupled between two reflective structuresaccording to embodiments disclosed herein.

FIG. 8 illustrates a different SAW CRF structure that includes aplurality of IDTs that are longitudinally coupled between two reflectivestructures according to embodiments disclosed herein.

FIG. 9A illustrates a different SAW CRF structure that includes aplurality of IDTs that are longitudinally coupled between two reflectivestructures according to embodiments disclosed herein.

FIG. 9B illustrates an alternative configuration for the SAW CRFstructure of FIG. 9A.

FIG. 10 illustrates a different SAW CRF structure that includes aplurality of IDTs that are longitudinally coupled between two reflectivestructures according to embodiments disclosed herein.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

The present disclosure relates to acoustic wave devices, andparticularly to interdigital transducer (IDT) arrangements for surfaceacoustic wave (SAW) devices. Representative SAW devices are describedherein that provide sharp transitions between passband frequencies andfrequencies that are outside of desired passbands. In certainembodiments, a SAW device may include several IDTs arranged betweenreflective structures and one or more additional IDTs or electrode pairsthat are configured to modify the influence of parasitic capacitance, orother internal device capacitance, thereby improving steepness on theupper side of a passband as well as improving rejection for frequenciesoutside of the passband. The one or more additional IDTs or electrodepairs may be configured as at least one of a capacitor, an IDTcapacitor, an IDT with a floating electrode, or combinations thereof.

Before describing particular embodiments of the present disclosurefurther, a general discussion of SAW devices is provided. FIG. 1 is aperspective view illustration of a representative SAW device 10. The SAWdevice 10 includes a substrate 12, a piezoelectric layer 14 on thesubstrate 12, an IDT 16 on a surface of the piezoelectric layer 14opposite the substrate 12, a first reflector structure 18A on thesurface of the piezoelectric layer 14 adjacent to the IDT 16, and asecond reflector structure 18B on the surface of the piezoelectric layer14 adjacent to the IDT16 opposite the first reflector structure 18A.

The IDT 16 includes a first electrode 20A and a second electrode 20B,each of which include a number of electrode fingers 22 that areinterleaved with one another as shown. The first electrode 20A and thesecond electrode 20B may also be referred to as comb electrodes. Alateral distance between adjacent electrode fingers 22 of the firstelectrode 20A and the second electrode 20B defines an electrode pitch Pof the IDT 16. The electrode pitch P may at least partially define acenter frequency wavelength A of the SAW device 10, where the centerfrequency is the primary frequency of mechanical waves generated in thepiezoelectric layer 14 by the IDT 16. For a single electrode IDT 16 suchas the one shown in FIG. 1, the center frequency wavelength λ is equalto twice the electrode pitch P. For a double electrode IDT 16, thecenter frequency wavelength λ is equal to four times the electrode pitchP. A finger width W of the adjacent electrode fingers 22 over theelectrode pitch P may define a metallization ratio, or duty factor, ofthe IDT 16, which may dictate certain operating characteristics of theSAW device 10.

In operation, an alternating electrical input signal provided at thefirst electrode 20A is transduced into a mechanical signal in thepiezoelectric layer 14, resulting in one or more acoustic waves therein.In the case of the SAW device 10, the resulting acoustic waves arepredominately surface acoustic waves. As discussed above, due to theelectrode pitch P and the metallization ratio of the IDT 16, thecharacteristics of the material of the piezoelectric layer 14, and otherfactors, the magnitude and frequency of the acoustic waves transduced inthe piezoelectric layer 14 are dependent on the frequency of thealternating electrical input signal. This frequency dependence is oftendescribed in terms of changes in the impedance and/or a phase shiftbetween the first electrode 20A and the second electrode 20B withrespect to the frequency of the alternating electrical input signal. Analternating electrical potential between the two electrodes 20A and 20Bcreates an electrical field in the piezoelectric material which generateacoustic waves. The acoustic waves travel at the surface and eventuallyare transferred back into an electrical signal between the electrodes20A and 20B. The first reflector structure 18A and the second reflectorstructure 18B reflect the acoustic waves in the piezoelectric layer 14back towards the IDT 16 to confine the acoustic waves in the areasurrounding the IDT 16.

The substrate 12 may comprise various materials including glass,sapphire, quartz, silicon (Si), or gallium arsenide (GaAs) among others,with Si being a common choice. The piezoelectric layer 14 may be formedof any suitable piezoelectric material(s). In certain embodimentsdescribed herein, the piezoelectric layer 14 is formed of lithiumtantalate (LT), or lithium niobate (LiNbO₃), but is not limited thereto.In certain embodiments, the piezoelectric layer 14 is thick enough orrigid enough to function as a piezoelectric substrate. Accordingly, thesubstrate 12 in FIG. 1 may be omitted. Those skilled in the art willappreciate that the principles of the present disclosure may apply toother materials for the substrate 12 and the piezoelectric layer 14. TheIDT 16, the first reflector structure 18A, and the second reflectorstructure 18B may comprise aluminum (Al). While not shown to avoidobscuring the drawings, additional passivation layers, frequencytrimming layers, or any other layers may be provided over all or aportion of the exposed surface of the piezoelectric layer 14, the IDT16, the first reflector structure 18A, and the second reflectorstructure 18B. Further, one or more layers may be provided between thesubstrate 12 and the piezoelectric layer 14 in various embodiments.

SAW devices may be configured in so-called coupled resonator filter(CRF) or double mode SAW (DMS) filter arrangements. A typical CRF isdesigned by placing several IDTs between two reflective structures, orgratings. FIG. 2A illustrates an example SAW CRF structure 24 thatincludes a plurality of IDTs 26-1 to 26-5 that are longitudinallycoupled between two reflective structures 28-1, 28-2. A substrate (e.g.,12 of FIG. 1) and piezoelectric layer (e.g., 14 of FIG. 1) are notshown. The IDTs 26-1, 26-3, and 26-5 are electrically connected to aninput signal and ground, and may therefore be referred to as input IDTs.The IDTs 26-2, 26-4 are electrically connected to an output signal andground, and may be referred to as output IDTs. The input IDTs 26-1,26-3, and 26-5 are configured in an alternating arrangement between thetwo reflective structures 28-1, 28-2. In operation, surface acousticwaves are generated by the input IDTs 26-1, 26-3, and 26-5 in responseto an input signal and the surface acoustic waves are acousticallycoupled to the output IDTs 26-2, 26-4 where they are converted back toan output signal. As discussed above, the electrode pitch and themetallization ratio of the plurality of IDTs 26-1 to 26-5, thecharacteristics of the material of the underlying piezoelectric layer,and other factors influence the magnitude and frequency of the acousticwaves transduced and filtered by the SAW CRF structure 24. It isdesirable for the SAW CRF structure 24 to highly attenuate or rejectfrequencies outside of a desired passband. In practice, an internal orparasitic capacitance within the SAW CRF structure 24 may exist betweenthe input IDTs 26-1, 26-3, and 26-5 and the output IDTs 26-2, 26-4. Thiscapacitance can limit the rejection response of the SAW CRF structure24, particularly at frequencies above the passband, where a shoulder maybe visible in plots of the frequency response. One way to reduce theinfluence of this capacitance is to place a capacitor 30 that iselectrically coupled between the input signal and the output signal andoutside of a cavity between the two reflective structures 28-1, 28-2. Ineffect, this creates electrical zeros on either side of the passbandwhile coupling adjacent resonance modes within the cavity between thetwo reflective structures 28-1, 28-2. In some examples, the capacitor 30can include an IDT connected between the input signal and the outputsignal outside of the reflective structures 28-1, 28-2.

While providing improvement in the rejection response above a desiredpassband, the use of a capacitor as illustrated in FIG. 2A does haveperformance limitations. FIG. 2B is an S-Parameters plot representingsimulations of the SAW CRF structure 24 of FIG. 2A with a variety ofcapacitor 30 values. The S-parameter magnitude is plotted in decibels(dB) across a megahertz (MHz) frequency range. Insertion loss, or S2,1,is an indication of how much power is transferred. For frequencies whereS2,1 is at or near 0 dB, then substantially all power from a signal istransferred. Accordingly, a passband is illustrated where the S2,1values are at or near 0 dB. On either side of the passband, or theshoulder regions, the S2,1 values decrease rapidly. As the S2,1 valuebecomes farther away from 0 dB, more and more power is reflected and/orattenuated. For example, a value of −40 dB reflects more power than avalue of −20 dB. FIG. 2B represents model simulations for the SAW CRFstructure 24 of FIG. 2A with the capacitor 30 values starting at 0.0picofarad (pF), or no capacitor, and progressively increasing to valuesof 0.2 pF, 0.4 pF, 0.6 pF, 0.8 pF, and 1.0 pF. As illustrated, acapacitor 30 value of 0.0 pF provides a shoulder above the passband thathas a gradual slope. As the capacitor 30 values progressively increasefrom 0.2 pF to 1.0 pF, the gradual shoulder is steadily decreased toprovide a steeper transition between passing frequencies and attenuatedor filtered frequencies. Despite the improved shoulder steepness for thepassband, a trade-off exists for increasing capacitor 30 values. Asshown in the higher frequency ranges above the passband and shoulderregion, such as between about 800 MHz and 850 MHz range, each increasingcapacitor 30 value negatively impacts the rejection response.

According to embodiments disclosed herein, a SAW device may comprise apiezoelectric material, at least one input IDT on the piezoelectricmaterial and electrically connected to an input signal and ground, atleast one output IDT on the piezoelectric material and electricallyconnected to an output signal and ground, and an additional IDT on thepiezoelectric material and located between an input IDT and an outputIDT. The additional IDT may comprise corresponding electrodes that arerespectively connected to the input signal and the output signal for theSAW device. In this manner, the additional IDT may alter an internaldevice capacitance to provide a sharper transition, or improved passbandsteepness, between frequencies in and out of a passband. Additionally,by placing the additional IDT between the input IDT and the output IDT,rejection of frequencies further above the passband may also beimproved.

FIG. 3 illustrates a SAW CRF structure 32 that includes a plurality ofIDTs 34-1 to 34-9 that are longitudinally coupled between two reflectivestructures 36-1, 36-2. A substrate (e.g., 12 of FIG. 1) and apiezoelectric layer (e.g., 14 of FIG. 1) are not shown. Each of the IDTs34-1, 34-5, 34-9 comprise corresponding electrodes that are electricallyconnected to an input signal and ground, and may be referred to as inputIDTs. Each of the IDTs 34-3, 34-7 comprise corresponding electrodes thatare electrically connected to an output signal and ground, and may bereferred to as output IDTs. As illustrated in FIG. 3, the input IDTs34-1, 34-5, 34-9 and the output IDTs 34-3, 34-7 may be configured in analternating arrangement between the two reflective structures 36-1,36-2. The IDTs 34-2, 34-4, 34-6, 34-8 are additional IDTs that areelectrically connected to the input signal and the output signal. Inthis manner, the additional IDTs 34-2, 34-4, 34-6, 34-8 are neitherinput IDTs nor output IDTs. In particular, each of the additional IDTs34-2, 34-4, 34-6, 34-8 comprises an electrode pair that includes acorresponding first electrode 38-2, 38-4, 38-6, 38-8 electricallyconnected to the input signal and a corresponding second electrode 40-2,40-4, 40-6, 40-8 electrically connected to the output signal.Accordingly, the additional IDTs 34-2, 34-4, 34-6, 34-8 comprise IDTcapacitors that alter the internal device capacitance to provide asharper transition, or improved passband steepness, between frequenciesin and out of the passband. The additional IDTs 34-2, 34-4, 34-6, 34-8may be configured between each pair of alternating input IDTs 34-1,34-5, 34-9 and output IDTs 34-3, 34-7. For example, the additional IDT34-2 is configured between the input IDT 34-1 and the output IDT 34-3,the additional IDT 34-4 is configured between output IDT 34-3 and theinput IDT 34-5, and so on. In operation, surface acoustic waves that aregenerated by the input IDTs 34-1, 34-5, 34-9 in response to an inputsignal are acoustically coupled to the output IDTs 34-3, 34-7 throughthe additional IDTs 34-2, 34-4, 34-6, 34-8. In this manner, theadditional IDTs 34-2, 34-4, 34-6, 34-8 also influence the passband ofthe device and may be configured to improve rejection performanceoutside of the passband. For example, the additional IDTs 34-2, 34-4,34-6, 34-8 may be designed to acoustically pass only frequencies withina desired passband, thereby altering the phase of frequencies outside ofthe passband. One or more of the additional IDTs 34-2, 34-4, 34-6, 34-8may be placed in various positions between the reflective structures36-1, 36-2 depending on the desired passband of a particularapplication. In this regard, the location of electrical zeros and/orpoles within the SAW CRF structure 32 can be tailored for variousapplications. In certain embodiments, one or more of the plurality ofIDTs 34-1 to 34-9 may comprise a metallization ratio, or duty factor, ofany range between 0 and 1 of a center wavelength A. In certainembodiments, the metallization ration is in a range of about 0.1 toabout 0.9; or in a range of about 0.2 to about 0.8; or in a range ofabout 0.3 to about 0.7; or in a range of about 0.4 to about 0.5. Incertain embodiments, the metallization ratio comprises a value of about0.4, or a value of about 0.5. For simplicity, FIG. 3 as well as figuresfor subsequent embodiments, illustrate the plurality of IDTs 34-1 to34-9 as unapodized IDTs where each of the IDT electrode fingers has auniform length. In certain embodiments, one or more of the plurality ofIDTs 34-1 to 34-9 may comprise an apodized IDT where electrode fingershave different lengths at different positions along the apodized IDTthat are configured for a particular response function.

SAW devices according to embodiments disclosed herein may beincorporated within larger devices and systems to provide simplifiedlayouts or topologies. FIGS. 4A, 4B, 5A, and 5B illustraterepresentative radio frequency (RF) duplexing devices with various SAWCRF devices as disclosed herein. RF duplexing devices typically areconfigured to receive signals and transmit signals of a different bandusing a common antenna. One of the primary challenges of duplexing isthat RF transmission signals and RF receive signals can interfere withone another and accordingly, RF duplexing devices may employ one or morefilters to improve isolation.

FIG. 4A is a block diagram of an RF duplexer 42 that includes the SAWCRF structure 24 of FIG. 2A. The RF duplexer 42 includes a transmit (TX)port, a receive (RX) port, and an antenna (ANT) port. A TX filter 44 ispositioned between the TX port and the antenna port and an RX filter 46is positioned between the RX port and the antenna port. The TX filter 44is configured as a ladder filter with series resonators TX1, TX3, TX5and shunt resonators TX2, TX4, TX6. The RX filter 46 includes seriesresonators RX1, RX3, and a shunt resonator RX2 as well as the SAW CRFstructure 24 as previously described for FIG. 2A. The SAW CRF structure24 includes five IDTs that alternate between input IDTs and output IDTsand a capacitor 48 is connected between the input and output of the SAWCRF structure 24. FIG. 4B is a block diagram of an RF duplexer 50 thatincludes the SAW CRF structure 32 of FIG. 3. The RF duplexer 50 includesthe TX filter 44 of FIG. 4A between the TX port and the antenna port,but an RX filter 52 that is different. The RX filter 52 includes the SAWCRF structure 32 where an additional IDT as previously described ispositioned between each of the five total alternating input IDTs andoutput IDTs. In this regard, the capacitor 48 and the series resonatorRX3 of FIG. 4A may be omitted, thereby saving costs and die space indevice layouts.

FIG. 5A is a top view of a device layout of the RF duplexer 42 of FIG.4A. As illustrated, the RF duplexer 42 includes the resonators TX1 toTX6, the resonators RX1 to RX3, the SAW CRF structure 24, and thecapacitor 48 as previously described as well as areas for RX, TX,antenna, and various ground connections. FIG. 5B is a top view of adevice layout of the RF duplexer 50 of FIG. 4B. As illustrated, the RFduplexer 50 includes the resonators TX1 to TX6, the resonators RX1 toRX2, and the SAW CRF structure 32 as previously described as well asareas for RX, TX, antenna, and various ground connections. Due to theconfiguration of the SAW CRF structure 32, the RF duplexer 50 does notinclude the capacitor 48 and the resonator RX3 of FIG. 5A. Additionally,the series resonator RX1 may have a reduced size. In this regard, thereis noticeably improved die space savings between the SAW CRF structure32 and the resonator RX2 as well as between the resonator RX1 and theground connection for the resonator RX2.

FIGS. 6A and 6B are plots comparing the performance of RF duplexers withvarious SAW CRF structures as disclosed herein. In FIGS. 6A and 6B,Duplexer 1 refers to the RF duplexer 50 of FIG. 4B that includes the SAWCRF structure 32 according to embodiments disclosed herein. Duplexer 2refers to the RF duplexer 42 of FIG. 4A that includes the SAW CRFstructure 24 and the capacitor 48. For the sake of comparison, Duplexer3 was included and refers to the RF duplexer 42 of FIG. 4A, but with theseries resonator RX3 removed. In this regard, a comparison of Duplexer 1and Duplexer 3 is useful to highlight the influence of just replacingthe SAW CRF structure 24 and the capacitor 48 of FIG. 4A with the SAWCRF structure 32 of FIG. 4B. FIG. 6A is a comparison plot for duplexerisolation in dB for Duplexers 1, 2, and 3, where a lower value indicatesbetter isolation. As illustrated, Duplexer 1 has noticeably betterisolation (e.g. 5 dB or more) than Duplexer 3, particularly in thefrequency range above 778 MHz. Additionally, Duplexers 1 and 2 showsimilar isolation values across the frequency range. FIG. 6B is acomparison plot for the passband of the Duplexers 1, 2, and 3. Asdescribed for FIG. 2B, a passband is illustrated where the plot valuesare at or near 0 dB with shoulder regions on either side where the plotvalues noticeably decrease from 0 dB. As previously described, it isdesirable to have a passband with sharp or steep shoulders thattransition to high rejection performance on either side of the passband.As illustrated, Duplexer 1 shows a steep shoulder on the high frequencyside of the passband and has noticeably improved rejection for regionsabove and below the passband. In particular, Duplexer 1 demonstrates animprovement of at least 2 dB or more for frequencies in the range ofabout 817 MHz to about 828 MHz.

As previously described, a SAW device may comprise at least oneadditional IDT located between an input IDT and an output IDT on apiezoelectric material. In certain embodiments, the at least oneadditional IDT may include an IDT capacitor with a floating electrode.FIG. 7 illustrates a SAW CRF structure 54 that includes a plurality ofIDTs 56-1 to 56-9 that are longitudinally coupled between two reflectivestructures 57-1, 57-2. A substrate (e.g. 12 of FIG. 1) and apiezoelectric layer (e.g., 14 of FIG. 1) are not shown. As previouslydescribed, each of the IDTs 56-1, 56-5, 56-9 comprise correspondingelectrodes that are electrically connected to an input signal andground, and may be referred to as input IDTs. Each of the IDTs 56-3,56-7 comprise corresponding electrodes that are electrically connectedto an output signal and ground, and may be referred to as output IDTs.As illustrated in FIG. 7, the input IDTs 56-1, 56-5, 56-9 and the outputIDTs 56-3, 56-7 may be configured in an alternating arrangement betweenthe two reflective structures 57-1, 57-2. The IDTs 56-2, 56-4, 56-6,56-8 are additional IDTs that are electrically connected to the inputsignal and the output signal. In this manner, the additional IDTs 56-2,56-4, 56-6, 56-8 are neither input IDTS nor output IDTs. In particular,each of the additional IDTs 56-2, 56-4, 56-6, 56-8 comprises anelectrode pair that includes a corresponding first electrode 58-2, 58-4,58-6, 58-8 electrically connected to the input signal and acorresponding second electrode 60-2, 60-4, 60-6, 60-8 electricallyconnected to the output signal. Each of the additional IDTs 56-2, 56-4,56-6, 56-8 also includes a corresponding floating electrode 62-2, 62-4,62-6, 62-8 in between the first electrode 58-2, 58-4, 58-6, 58-8 and thesecond electrode 60-2, 60-4, 60-6, 60-8. Each floating electrode 62-2,62-4, 62-6, 62-8 is not directly connected to either of the input signalor the output signal, and may therefore be referred to as floatingvoltage electrodes. Accordingly, the additional IDTs 56-2, 56-4, 56-6,56-8 comprise IDT capacitors with floating electrodes that mayeffectively form multiple capacitors in series within each of theadditional IDTs 56-2, 56-4, 56-6, 56-8. In this manner, the additionalIDTs 56-2, 56-4, 56-6, 56-8 may alter the internal device capacitance toprovide a sharper transition, or improved passband steepness, betweenfrequencies in and out of the passband.

As previously described, a SAW device may comprise at least oneadditional IDT located between an input IDT and an output IDT on apiezoelectric material. In certain embodiments, the at least oneadditional IDT may include electrodes with alternative shapes. FIG. 8illustrates a SAW CRF structure 64 that includes a plurality of IDTs66-1 to 66-9 that are acoustically and longitudinally coupled betweentwo reflective structures 67-1, 67-2. A substrate (e.g. 12 of FIG. 1)and a piezoelectric layer (e.g., 14 of FIG. 1) are not shown. The IDTs66-1, 66-5, 66-9 are input IDTs and the IDTs 66-3, 66-7 are output IDTsas previously described. The IDTs 66-2, 66-4, 66-6, 66-8 are additionalIDTs that are electrically connected to the input signal and the outputsignal, or IDT capacitors as previously described. Each of theadditional IDTs 66-2, 66-4, 66-6, 66-8 comprises an electrode pair thatincludes a corresponding first electrode 68-2, 68-4, 68-6, 68-8electrically connected to the input signal and a corresponding secondelectrode 70-2, 70-4, 70-6, 70-8 electrically connected to the outputsignal. In FIG. 8, the first electrode 68-2, 68-4, 68-6, 68-8 and thesecond electrode 70-2, 70-4, 70-6, 70-8 comprise elongated fingers thatare non-linear. For example, the first electrode 68-2 extends from aninput signal line and includes two ninety-degree turns to form a Ushape. In a similar manner, the second electrode 70-2 forms an invertedU shape that is interdigitated with the first electrode 68-2. In thisregard, the area where the first electrode 68-2 and the second electrode70-2 are close to each other is increased. In certain embodiments, otherelectrode shapes are possible. For example, the first electrode 68-2 andthe second electrode 70-2 may have curved turns to form a U shape. Incertain embodiments, either the first electrode 68-2 or the secondelectrode 70-2 may comprise a linear shape and the other of firstelectrode 68-2 or the second electrode 70-2 comprises a non-linearshape. For example, the first electrode 68-2 may comprise a linear shapeand the second electrode 70-2 may comprise a U shape that extends aroundthe first electrode 68-2.

In certain embodiments, a SAW device may comprise at least oneadditional IDT located between an input IDT and an output IDT on apiezoelectric material and the at least one additional IDT is notdirectly connected to either input or output signals. In certainembodiments, the at least one additional IDT may include a firstelectrode that is connected to ground and a second electrode that isfloating. FIG. 9A illustrates a SAW CRF structure 72 that includes aplurality of IDTs 74-1 to 74-9 that are longitudinally coupled betweentwo reflective structures 76-1, 76-2. A substrate (e.g., 12 of FIG. 1)and a piezoelectric layer (e.g. 14 of FIG. 1) are not shown. The IDTs74-1, 74-5, 74-9 are input IDTs and the IDTs 74-3, 74-7 are output IDTsas previously described. In FIG. 9A, the IDTs 74-2, 74-4, 74-6, 74-8 areadditional IDTs that are not directly connected to the input signal orthe output signal. Each of the additional IDTs 74-2, 74-4, 74-6, 74-8comprises an electrode pair that includes a corresponding firstelectrode 78-2, 78-4, 78-6, 78-8 electrically connected to ground and acorresponding second electrode 80-2, 80-4, 80-6, 80-8 that is floating.An individual one of the additional IDTs 74-2, 74-4, 74-6, 74-8 ispositioned between corresponding pairs of the input IDTs 74-1, 74-5,74-9 and the output IDTs 74-3, 74-7. Accordingly, a capacitance betweenthe input IDTs 74-1, 74-5, 74-9 and the output IDTs 74-3, 74-7 isreduced, thereby altering the internal device capacitance to provide asharper transition, or improved passband steepness, between frequenciesin and out of the passband. In certain embodiments, each of the secondelectrodes 80-2, 80-4, 80-6, 80-8 are connected with each other.

FIG. 9B illustrates an alternative configuration for the SAW CRFstructure 72 of FIG. 9A. In FIG. 9B, common elements are numbered thesame as in FIG. 9A and the description of the common elements providedabove for FIG. 9A may also be applicable to FIG. 9B. In FIG. 9B, thefirst electrodes 78-2, 78-4, 78-6, 78-8 and the second electrodes 80-2,80-4, 80-6, 80-8 comprise electrodes that are devoid of electrodefingers. In certain embodiments, the first electrodes 78-2, 78-4, 78-6,78-8 and the second electrodes 80-2, 80-4, 80-6, 80-8 compriserectangular, square, or other solid shapes. In certain embodiments, atleast one of the first electrodes 78-2, 78-4, 78-6, 78-8 and acorresponding one of the second electrodes 80-2, 80-4, 80-6, 80-8comprise L shapes. In this regard, the SAW CRF structure 72 includes anadditional electrode pair 81-2, 81-4, 81-6, 81-8 arranged between theinput IDTs 74-1, 74-5, 74-9 and the output IDTs 74-3, 74-7 that isconfigured to alter the internal or parasitic capacitance of the SAW CRFstructure 72.

In certain embodiments, a SAW device may comprise a first reflectivestructure and a second reflective structure on a piezoelectric materialwith a plurality of input IDTs and a plurality of output IDTs arrangedbetween the first reflective structure and the second reflectivestructure. The plurality of input IDTs and the plurality of output IDTsmay be configured in an alternating arrangement between the firstreflective structure and the second reflective structure, and aplurality of additional IDTs is arranged between corresponding ones ofthe plurality of input IDTs and corresponding ones of the plurality ofoutput IDTs. In certain embodiments, at least one additional IDT of theplurality of additional IDTs is electrically connected to an inputsignal and an output signal. In certain embodiments, at least one otheradditional IDT of the plurality of additional IDTs is not directlyelectrically connected to either of the input signal and the outputsignal.

FIG. 10 illustrates a SAW CRF structure 82 that includes a plurality ofIDTs 84-1 to 84-9 that are acoustically and longitudinally coupledbetween two reflective structures 86-1, 86-2. A substrate (e.g., 12 ofFIG. 1) and a piezoelectric layer (e.g., 14 of FIG. 1) are not shown.The IDTs 84-1, 84-5, 84-9 are input IDTs and the IDTs 84-3, 84-7 areoutput IDTs as previously described. In FIG. 10, the IDTs 84-2, 84-4,84-8 are additional IDTs that are not directly connected to the inputsignal or the output signal. In certain embodiments, each of theadditional IDTs 84-2, 84-4, 84-6, 84-8 comprises an electrode pair thatincludes a corresponding first electrode 88-2, 88-4, 88-6, 88-8 and acorresponding second electrode 90-2, 90-4, 90-6, 90-8. Notably, theadditional IDTs 84-2, 84-4, 84-6, 84-8 may include different types ofIDTs. For example, the additional IDT 84-6 is electrically connected tothe input signal and the output signal. In this regard, the additionalIDT 84-6 comprises a first electrode 88-6 that is electrically connectedto the input signal and a second electrode 90-6 that is electricallyconnected to the output signal. Accordingly, the additional IDT 84-6 isan IDT capacitor that alters the internal device capacitance aspreviously described. In further embodiments, the additional IDT 84-6may comprise a floating electrode between the first electrode 88-6 andthe second electrode 90-6 as previously described. In contrast to theadditional IDT 84-6, the additional IDTs 84-2, 84-4, 84-8 are notdirectly electrically connected to either of the input signal and theoutput signal. The additional IDTs 84-2, 84-4, 84-8 instead comprise thecorresponding first electrode 88-2, 88-4, 88-8 connected to ground andthe corresponding second electrode 90-2, 90-4, 90-8 that is a floatingelectrode, or a floating voltage electrode. The additional IDTs 84-2,84-4, 84-8 are positioned between corresponding ones of the input IDTs84-1, 84-5, 84-9 and the output IDTs 84-3, 84-7, thereby reducing acapacitance between the input IDTs 84-1, 84-5, 84-9 and the output IDTs84-3, 84-7 as previously described.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A surface acoustic wave (SAW) device, comprising:a piezoelectric material; at least one input interdigital transducer(IDT) on the piezoelectric material and electrically connected to aninput signal and ground; at least one output IDT on the piezoelectricmaterial and electrically connected to an output signal and ground; andan additional IDT on the piezoelectric material and electricallyconnected to the input signal and the output signal, wherein theadditional IDT is arranged between the at least one input IDT and the atleast one output IDT, and the additional IDT comprises interleavedelectrode fingers.
 2. The SAW device of claim 1, wherein the additionalIDT comprises an IDT capacitor.
 3. The SAW device of claim 1, whereinthe additional IDT comprises a first electrode electrically connected tothe input signal and a second electrode electrically connected to theoutput signal.
 4. The SAW device of claim 1, further comprising a firstreflective structure and a second reflective structure on thepiezoelectric material, wherein the at least one input IDT, the at leastone output IDT and the additional IDT are arranged between the firstreflective structure and the second reflective structure.
 5. The SAWdevice of claim 1, wherein the at least one input IDT comprises aplurality of input IDTs and the at least one output IDT comprises aplurality of output IDTs.
 6. The SAW device of claim 5 wherein theplurality of input IDTs and the plurality of output IDTs are configuredin an alternating arrangement.
 7. The SAW device of claim 1, wherein atleast one of the at least one input IDT, the at least one output IDT,and the additional IDT comprises an apodized IDT.
 8. A surface acousticwave (SAW) device, comprising: a piezoelectric material; a firstreflective structure and a second reflective structure on thepiezoelectric material; a plurality of input interdigital transducers(IDTs) and a plurality of output IDTs arranged on the piezoelectricmaterial and between the first reflective structure and the secondreflective structure, wherein the plurality of input IDTs and theplurality of output IDTs are configured in an alternating arrangementbetween the first reflective structure and the second reflectivestructure; and a plurality of additional IDTs arranged betweencorresponding ones of the plurality of input IDTs and corresponding onesof the plurality of output IDTs, wherein at least one additional IDT ofthe plurality of additional IDTs is electrically connected to an inputsignal and an output signal, and the at least one additional IDT of theplurality of additional IDTs comprises interleaved electrode fingers. 9.The SAW device of claim 8, wherein the plurality of additional IDTscomprises at least two additional IDTs electrically connected to theinput signal and the output signal.
 10. The SAW device of claim 8,wherein at least one of the plurality of input IDTs, the plurality ofoutput IDTs, and the plurality of additional IDTs comprises ametallization ratio in a range of about 0.2 to about 0.8.
 11. The SAWdevice of claim 8, wherein at least one of the plurality of input IDTs,the plurality of output IDTs, and the plurality of additional IDTscomprises an apodized IDT.
 12. The SAW device of claim 8, wherein atleast one other additional IDT of the plurality of additional IDTs isnot directly electrically connected to either of the input signal andthe output signal.
 13. The SAW device of claim 12, wherein the at leastone other additional IDT of the plurality of additional IDTs comprises afirst electrode electrically connected to ground and a second electrodethat is a floating electrode.